My raspberry bushes have, for several years now, developed these raised, yellow, powdery spots on some leaves. It seems to be getting worse each year. I don't know how early in the season it's started in previous years, but I first noticed this year's first infected leaves last week. I have never noticed the yellow spots developing on the berries themselves. Although I do get quite a few small, dried out berries, and sometimes a lot of berries mold on the bush. Removing the plants and getting new ones isn't really practical, nor is there an alternate location in my yard to start over if this is something that stays in the soil. Any help identifying this (is this late leaf rust?) and suggestions on how to treat would be greatly appreciated!!
It does look like a rust. The best control is very careful fall/winter clean up- remove all fruited canes and fallen leaves and destroy them (not compost). A delayed dormant spray, when the leaves first begin to emerge in spring, can also help. Commercial growers also till between the rows to turn under old leaves that might carry the rust spores- applying a new mulch every spring effectively does the same thing.
